Magnetic keyboard

ABSTRACT

A magnetic keyboard assembly including a key stem magnetically held in an unactuated position by the attraction of a magnet to a metallic mounting board and adapted to be reciprocated between an unactuated position and an actuated position where an electrically conductive rubber grommet engages a contact pad having spaced-apart contacts which become electrically connected upon engagement of the electrically conductive grommet. The grommet is characterized by a resilient outer ring spaced from a center portion by a resilient web with the outer rim engaging the contacts first so that the outer ring slidably engages the spaced contacts as the center portion moves toward engagement with the contact pad, thus providing not only good operator touch to the keyboard but also assuring clear electrical contact by the slidable rubbing action of the outer ring.

United States Patent 1 Pedersen et al.

[ 1 Oct. 28, 1975 MAGNETIC KEYBOARD [73] Assignee: The Singer Company,New York,

[22] Filed: Aug. 9, 1974 [21] Appl. No.: 495,981

[52] US. Cl 335/205; 200/159 B; 200/243 [51] Int. Cl. H01H 9/00 [58]Field of Search 335/205, 206, 207', 200/5 R, 5 A, 159 B, 264, 243

[56] References Cited I UNITED STATES PATENTS 3,668,356 6/1972 Kekas200/159 B X 3,699,294 10/1972 Sudduth 200/243 3,705,276 12/1972 Seegeret a1. 200/5 A 3,721,778 3/1973 Seeger et al 200/5 R 3,728,509 4/1973Shimojo 200/264 3,736,397 5/1973 Pedersen 335/206 X Primary ExaminerG.Harris Attorney, Agent, or Firm-Joseph R. Dwyer [57] ABSTRACT A magnetickeyboard assembly including a key stem magnetically held in anunactuated position by the attraction of a magnet to a metallic mountingboard and adapted to be reciprocated between an unactuated position andan actuated position where an electrically conductive rubber grommetengages a contact pad having spaced-apart contacts which becomeelectrically connected upon engagement of the electrically conductivegrommet. The grommet is characterized by a resilient outer ring spacedfrom a center portion by a resilient web with the outer rim engaging thecontacts first so that the outer ring slidably engages the spacedcontacts as the center portion moves toward engagement with the contactpad, thus providing not only good operator touch to the keyboard butalso assuring clear" electrical contact by the slidable rubbing actionof the outer ring.

8 Claims, 6 Drawing Figures US. Patent Oct. 28, 1975 3,916,360

MAGNETIC KEYBOARD BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to keyboards used for a variety of applications,such as calculators, computers, electronic cash registers, and otherdevices for home or office use.

2. Description of the Prior Art A typical magnetic latching and magneticswitch actuation keyboard is disclosed in U.S. Pat. No. 3,693,123 whichissued Sept. 19, 1972. As shown in this patent, a plurality of keyassemblies are mounted for reciprocating movement in a mounting plateassembly having an upper mounting plate and a lower base member. Theupper mounting plate is constructed of a material exhibiting lowmagnetic remanence, and is provided with an upper cushioning layer and alower spacing layer, both of resilient material. Each key assemblycomprises a key top, a non-magnetic key stem, a magnet mountedsubstantially transversely of the key stem below the lower spacinglayer, and a return spring positioned between the bottom surface of thekey top and the upper surface of the mounting plate. The base member isprovided with a plurality of magnetic reed switches, each associatedwith the individual magnets carried by the individual key stem. Each keyassembly is maintained in a non-actuated position by the combined forceof the return spring and the magnetic attraction between its magnet andthe mounting plate. When an individual key is depressed, the magnetcarried by the key stem is brought into close proximity with theassociated reed switch to actuate that particular reed switch. When theactuated key is released, the return spring and the magnetic attractionbetween the magnet and the mounting plate insures a return of the keyassembly to its non-actuated position.

An improvement in the field of magnetic keyboards and in key assembliesof U.S. Pat. No. 3,693,123, supra, is set forth in U.S. Pat. No.3,761,016, which issued on Sept. 25, 1973, in which there is disclosedand claimed an improved key stem magnet for eliminating magneticmigration in key assemblies. The improved key stem magnet has a slottedportion extending longitudinally thereof which provided a pair ofabutment edges which engage opposing surfaces of the key stem whenmounted in the key stem aperture. The abutment edges prevented axialmigration of the magnet in the key stem aperture.

These known keyboards eliminated the several disadvantages of the thenprior art and became known for their excellenttouch which, as set forthin the U.S. Pat. No. 3,693,123, supra, includes Breakaway Touch and StopTouch, all being performed with a Low Noise Factor. Breakaway Touch,Stop Touch and Low Noise Factor are the criteria for evaluating akeyboard from an operator point of view.

Breakaway Touch has been defined, in the aforesaid patent andincorporated in the keyboards disclosed therein, as that suitableresistance to the depression of a key which rapidly vanishes withcontinued key displacement. It must be sufficient to provide an operatorwith a sense that a given key has been broken away from its unac tuatedposition yet small enough so that when an operator actuates individualkeys repetitively thousands of times, it does not lead quickly tooperator fatigue.

Stop Touch has been defined, in the aforesaid patent and incorporated inthe keyboard disclosed therein, as that which the operator sensesthrough his fingertips that a given key has been depressed to the limitof its mechanical displacement without a highly undesirably joltingaction. This jolting action can be highly annoying to an operator andgreatly lessens the desirability of the keyboard.

And finally, Low Noise Factor has been defined, in the aforesaid patentand incorporated in the keyboard disclosed therein, as that minimumnoise level maintained in a keyboard so as to not produce distractingsounds which have been found to lead to operator errors.

Thus, having achieved a high performance in meeting the above criteriafor evaluating keyboards, the problem then became one of maintainingsuch high performance yet overcoming several disadvantages that havebeen found in such keyboards.

One of the disadvantages is that the assembly of the existing keyboardsrequired an intricate manufacturing procedure which, therefore,increased the cost of the keyboard. One such intricate assemblyprocedure is the alignment of the key stem magnets in such a manner thatthere would be no interference between magnets themselves and betweenthe magnets and the'reed switches, so that each reed switch would beresponsive to its associated key stem magnet only.

Another intricate assembly procedure in the manufacture of the existingkeyboards is the proper selection of the magnetic strength of themagnets, which selection required the taking into consideration of notonly the magnetic attraction to the mounting plate for proper BreakawayTouch and for maintenance of the key assembly at its unactuatedposition, but also equally important the sufficiency of the magnetism tooperate the individual reed switches associated therewith. Theseconsiderations thus can be said to require critical alignment of boththe megnets and the reed switches as well as a critical selection of themagnets themselves, all of which added to the cost of the keyboard.

Another disadvantage in the existing keyboards involved the magneticreed switches. While they operated satisfactorily, they are relativelyquite expensive and were prone to breakdown after prolonged operationand need replacement which, of course, made the cost of repair andmaintenance excessively high in addition to the high initialmanufacturing cost.

Accordingly, it is a primary object of this invention to improvemagnetic keyboards by maintaining their high performance yet reducingthe costs of manufacture and maintenance thereof.

SUMMARY OF THE INVENTION The foregoing disadvantages of the prior artare overcome and the foregoing objects accomplished by providing akeyboard having key assemblies which carry conductive rubber grommets ofa particular configuration which engage conductive contact pads, also ofa particular configuration, for providing the electrical connectionbetween the depressed key and the machine with which the keyboard isassociated. The combination of conductive rubber grommets and contactpads are in lieu of the magnetic reed switches of the existingkeyboards.

Like in the existing keyboards, each key assembly is reciprocablyreceived between a mounting member and a base member and each keyassembly includes a key top and a key stem with a key stem magnetcarried by the key stem. The mounting member comprises a plateconstructed of a material exhibiting low magnetic remanence and providedwith a resilient spacing layer selected to provide minimum noise levelfor each return key stroke and to provide predetermined maximum holdingforce between each key stem magnet and the plate, which results in theaforesaid Breakaway Touch. Disposed on the key stem between the magnetand the base member is a conductive rubber grommet which is also carriedby the key stem along with the magnet. Upon depression of an individualkey, the conductive rubber grommet contacts a conductive contact pad onthe base member, closing the circuit to the machine with which thekeyboard is associated. The conductive rubber grommet is provided withan outer rim which first engages the contact pad upon depression of thekey beforethe' main or center portion of the rubber grommet bottomsagainst the contact pad thereby providing a two-step'engagement with thecontact pad and also providing the Stop Touch to the keyboard. Thistwo-step contact with the contact pad tells the operator contact hasbeen made and that the key is fully depressed without the undesirablejolting action.

Accordingly, another advantage that will become apparent from thedetailed description hereinafter is that the outer rim of the rubbergrommet provides a rubbing action on the contact of the pad each time akey is depressed thus cleaning the contact pad to enable maximumconduction between the conductive rubber grommet and the conducting pad.

Another advantage inherent in the use of the rubber grommet is theelimination of the so-called upper cushioning layer of resilient foammaterial now on existing keyboards which heretofore provided the StopTouch but which, it has been found, was a continuous source ofdifficulty, one of which was the improper quality of the adhesiveutilized in trying to maintain this cushioning material in proper placeon the metal plate.

Now, for a fuller understanding of the nature and advantages of thisinvention, reference should be had to the following detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT Turning now to the drawings, FIG. 1' shows a keyboard with aplurality of numeric keys and function keys l2 grouped-in a fashionconvenient for an operator. Each key 12 is mounted on a mounting plate14 I explained in US. Pat. No. 3,693,123. The first function is theprovision of a maximum desired force for holding the key in anon-actuated or rest position by spacing key stem magnet 24 of keys 12from the layer 20 and that of reducing noise produced by the key whenreturned to its rest or unactuated position after being released by theoperator. The thickness and material selected for layer 22 is more fullyexplained in the aforesaid US. Pat. 3,693,123 supra.

Mounting plate 14 and base member 18 are each provided with a pluralityof apertures 26 and 28, which are slightly offset one from another torespectively receive in sliding relationship a suitable plastic key stem30 with its main body portion 32 and a lower body portion 34 of reduceddiameter and offset from the longitudinal axis of the key stem.

' Key assembly 12 is also provided with a suitable plastic key top 36having a groove 38 concentric with a central opening 40 to receive areturn spring 42. Key stem main body portion 32 has a pair oflongitudinally extending grooves 44 on two sides of the key stem and areof a length so that at least one groove will be exposed to the spacebelow the mounting plate whenever a key assembly is displaced to itsfull extent to provide unobstructed passage for the egress and intake ofair to the void below the key top to prevent the formation of a partialvacuum which wouldtend to retard return of the key assembly to the restposition.

The previously mentioned key stem magnet 24, which cooperates with thetwo layers20 and 22 to provide the Breakaway Touch and to hold the keyassembly at rest, as shown in FIG. 4, is mounted below the grooves 44 ina groove 46 on the main body portion 32 in a direction generallytransverse to the longitudinal axis of the key stem, as disclosed in theaforesaid US. Pat. No. 3,693,123; the magnet disclosed herein being ofthe type disclosed and claimed in the aforesaid US. Pat. No. 3,761,016.

Mounted below and abutting against the base 48 of the main body portion32 of the key stem by a press fit on the lower body portion 34 is aconductive rubber grommet 50 which cooperates with a conductive contactpad 52, which is more fully illustrated in FIG. 3. These conductiverubber grommets are made of a silicone rubber sold by Dow CorningCorporation, Midland, Michigan 48640 under the trademark Silas tic 2086.The base member 18 has a number of such contact pads 52, whichcorrespond in number to the number of key assemblies, and a number ofconductive lines 54 and 56 (two foreach conductive pad) whichelectrically interconnect to the various contact pads with a plugconnection (not shown) so that the entire keyboard will be electricallyconnected to the machine with which it is associated. The base member 18is constructed of a material selectable from a mimber of availablematerials commonly used for printed circuit boards, and the contact 52,togetherwiththe conductive lines 54, 54 and plug connection, are formedv on the base member by conventional photographic and etching processesknown to those skilled in the art.

Since the rubber grommet 50 and the conductive pads 52 form an importantaspect of this keyboard, at-

tention is now directed to FIGS. 2-6, which will now be described indetail.

In FIGS. 2, and 4-6 it can be seen that the rubber grommet 50 has arelatively large thick main or central portion 60 and a concentric outercircular ring-like outer rim 62 separated from the central portion by aweb 64 which is conical in cross-section, thicker where it joins thecenter portion 60 than it is where it joins the outer rim 62, so as tobend relatively freely as shown in FIG. 6 at 66. Center portion 60 isprovided with a central aperture 68 of a size selected to provide apress fit with the lower stem portion 34 when mounted on the key stem inabutting relationship with the base 18 of the key stem. As can beclearly seen in FIGS. 4-6, the lower or bottom side 70 of the centerportion 60 terminates above the lower curved edge 72 of the outer rim62. One purpose of the fore-shortened center portion 60 is to insurethat the outer rim edge 72 contacts the contact pad 52 first, on thedepression of an individual key, before the bottom 70 contacts the padupon continued depression of the key. This function is shown moreclearly in FIGS. 5 and 6. It is to He noted that, as the center portionis traveling toward the contact pad, after the initial contact by theouter rim edge 72, as shown in FIG. 5, the web 64, being resilient, willbend at its thinnest portion 66 adjacent the outer rim as shown in FIG.6. This causes a slightly outwardly rotating rubbing action by the loweredge on the contact pad which will continue until the key is fullydepressed. This rubbing action on the contact pad insures a continuedclean surface for proper electrical connection between the rubbergrommet and the contact pad 52.

Another purpose of the foreshortened center portion is the fact thatthis provides the Stop Touch feel to the key. An operator can feel theinitial contact and the overstroke by continued depression of the key,provides a feeling of safety that proper contact had been made. Also,almost the entire force placed on the key by the operator is taken bythe center portion which is not the original point of contact, so thatcontinued heavy pressure by an operator will not ruin the contacts ofthe contact pad.

Turning now to FIG. 3, which discloses the contact pad 52 in moredetail, it can be seen that the contact pad comprises two concentridcircular portions an inner ring 76 and an outer ring 78, both beingconcentric with the aperture 28 in the base member 18. Inner ring 76 isprovided with a plurality of radially outwardly extending ears 80 whichare interjacent with a plurality of radially inwardly extending ears 82on the outer ring 78 to provide therebetween an interstitialnonconductive gap 84. With inner ring 76 connected to one lead line 54and the outer ring 78 connected to another lead line 56, so that whenthe grommet bridges the gap 84 by contacting the pad 52, a circuit iscompleted between these two lead lines. The dotted line 86 in FIG. 3shows the relative size of the outer rim 62 arranged to bridge the gap84 between the extremities of the ears 80 and 82 when a key is depressedas shown in FIGS. 2, 5 and 6. One inherent advantage in providing anumber of ears is that the resistance developed through the rubbergrommet as it bridges each concentric individual gap between the pairsof ears is a parallel resistance connection with parallel connectedlines 54 and 56, so that an increase in the number of gaps bridgedbetween the interjacent ears actually reduces the resistance involved inthe electrical connection. Another advantage is that the chance ofmaking contact to perform the function is multiplied by at least thenumber of interstitial gaps offered to the conductive rubber grommet.

Thus, it becomes apparent that one of the advantages of the foregoingkeyboard assembly is the fact that the sole function now of the magnetmounted on the key stem is to hold the key assembly in its non-actuatedposition. Therefore, the selection and alignment of the magnets is notas critical as that of the prior art where the magnet also performed thefunction of actuating a reed switch when a selected key was selected anddepressed. It should also be noted that another inherent advantage inthis keyboard from a manufacturers point of view, is that the keyassembly itself, including the key top, key stem, return spring, etc.,need not be changed in any manner so that the dies, tools and jigs willby and large remain the same for the manufacture of the instantkeyboard.

Also, it should be noted further that the terms key and key assemblyhave been used interchangeably throughout the specification; keyassembly being used to described the combination of part, key top, keystern, grommet, etc., whereas key has often been used with its commonmeaning from the viewpoint of an operator who actuates keys of akeyboard.

Finally, while reference was made to the rubber grommet as being made ofSilastic 2086, any conductive elastomer of suitable resiliency andelectrical conductivity may be used to form the rubber grommets.

What is claimed is:

1. A magnetic keyboard comprising:

mounting means of magnetic material having an opening therein;

a key assembly including a key stem reciprocably mounted in said openingand a key top mounted at one end of said stern, said key assemblyadapted to be reciprocated between a non-actuated position and anactuatedposition;

magnetic means on said key stem and located on the opposite side of saidmounting means from said key P;

spacer means positioned between said mounting means and said magneticmeans for providing a predetermined maximum holding force therebetweenwhen said key is in said non-actuated position;

a base member from said mounting member and having an opening adapted toslidably receive one end of said key stern;

spaced-apart contact means, and a second means for engaging the contactpad, the bottom portion of which is spaced further from said contact padthan said first means when said key assembly is in the non-actuatedposition and thus only engages said contact pad upon further movement ofsaid key after initial contact by said first means.

2. The magnetic keyboard as claimed in claim 1 wherein said first meansof said grommet is so constructed and arranged to rub said spaced-apartcontact means as said second means engages said contact pad upon furthermovement of said keygso as to continually clean said contact means forcontinued enhancement of electrical conduction between said grommet andsaid'contact means.

i *The mag netic keyboard as claimed in claim 2 wherein said first meansof said grommet comprises an outer ring and said second means of saidgrommet comprises a center portion, said outer ring and center portionbeing separated by a resilient web, said center portion when engagingsaid contact pad taking the entire force of operator pressure on the keythus lessening possible damage to the contact means.

4. The magnetic keyboard as claimed in claim 3 wherein said outer ringslidably engages said spacedapart contact means.

' 5. The magnetic keyboard as claimed in claim 4 in which said contactpad comprises a pair of concentric rings with interadjacent earsproviding an interstitial non-conductive gap therebetween, which gap isbridged by said resilient electrically conductive means upon engagementwith said pad.

6. In a magnetic keyboard assembly including a key stem magneticallyheld in a non-actuated position,

an electrically conductive rubber grommet mounted on said key stem forelectrically connecting spaced-apart contacts of a contact pad in saidassembly when engaged by said grommet upon depression of said key withsufficient force to overcome the magnetic force holding said key in saidnon-actuatable position, said grommet having a first ring means forfirst contacting said spacedapart contacts upon initial engagementtherewith and a center portion for further engaging said contact padupon further depression of said key, said ringand said center portionbeing separated by a resilient web.

7. The grommet as claimed in claim 6 wherein said outer ring slidablyengages said spaced-apart contacts as said center portion moves towardengagement with said contact pad.

8. A magnetic keyboard comprising:

mounting means of magnetic material having an opening therein;

a key assembly including a key stem reciprocably mounted in said openingand a key top mounted at one end of said stem, said key assembly adaptedto be reciprocated between a non-actuated position and an actuatedposition;

magnetic means on said key stem and located on the opposite side of saidmounting means from said key P;

spacer means positioned between said mounting means and said magneticmeans for providing a predetermined maximum holding force therebetweenwhen said key is in said non-actuated position;

a base member spaced from said mounting member and having an openingadapted to slidably receive one end of said key stem;

a contact pad with spaced-apart contact means located on the side ofsaid base member facing said spacer means;

resilient electrically conductive means mounted on said key stem betweensaid magnetic means and said base member and engageable with saidspaced-apart contact means when said key is in its actuated position toelectrically connect said spaced-apart contact means;

said resilient electrically conductive means comprisa grommet having anouter ring and a center portion separated by a resilient web, thesurface of said ring facing said contact pad being closer to saidcontact pad than the surface of said center portion facing said contactpad so that said outer ring first slidably engages said spaced apartcontact means as said center portion moves toward engagement with saidcontact pad, the reaction force of said ring initially engaging saidcontact means being transmitted through said resilient web to said keystem and key top to provide the first step of a two-step touch to anoperator, and engagement of said center portion with said contact pad,and to provide the second step and stop touch to the operator, saidengagement of said center portion being directed to said key topindependently of said resilient web whereby continued pressure by theoperator on said key top is not transmitted to said ring, therebyeliminating possible damage to said spaced apart contact means by suchcontinued pressure of the operator.

1. A magnetic keyboard comprising: mounting means of magnetic materialhaving an opening therein; a key assembly including a key stemreciprocably mounted in said opening and a key top mounted at one end ofsaid stem, said key assembly adapted to be reciprocated between anon-actuated position and an actuated position; magnetic means on saidkey stem and located on the opposite side of said mounting means fromsaid key top; spacer means positioned between said mounting means andsaid magnetic means for providing a predetermined maximum holding forcetherebetween when said key is in said non-actuated position; a basemember spaced from said mounting member and having an opening adapted toslidably receive one end of said key stem; a contact pad withspaced-apart contact means located on the side of said base memberfacing said spacer means; resilient electrically conductive meansmounted on said key stem between said magnetic means and said basemember and engageable with said spaced-apart contact means when said keyis in its actuated position to electrically connect said spaced-apartcontact means; said resilient electrically conductive means comprising agrommet having a first means for contacting said spaced-apart contactmeans upon initial engagement therewith to electrically connect saidspaced-apart contact means, and a second means for engaging the contactpad, the bottom portion of which is spaced further from said contact padthan said first means when said key assembly is in the non-actuatedposition and thus only engages said contact pad upon further movement ofsaid key after initial contact by said first means.
 2. The magnetickeyboard as claimed in claim 1 wherein said first means of said grommetis so constructed and arranged to rub said spaced-apart contact means assaid second means engages said contact pad upon further movement of saidkey so as to continually clean said contact means for continuedenhancement of electrical conduction between said grommet and saidcontact means.
 3. The magnetic keyboard as claimed in claim 2 whereinsaid first means of said grommet comprises an outer ring and said secondmeans of said grommet comprises a center portion, said outer ring andcenter portion being separated by a resilient web, said center portionwhen engaging said contact pad taking the entire force of operatorpressure on the key thus lessening possible damage to the contact means.4. The magnetic keyboard as claimed in claim 3 wherein said outer ringslidably engages said spaced-apart contact means.
 5. The magnetickeyboard as claimed in claim 4 in which said contact pad comprises apair of concentric rings with interadjacent ears providing aninterstitial non-conductive gap therebetween, which gap is bridged bysaid resilient electrically conductive means upon engagement with saidpad.
 6. In a magnetic keyboard assembly including a key stemmagnetically held in a non-actuated position, an electrically conductiverubber grommet mounted on said key stem for electrically connectingspaced-apart contacts of a contact pad in said assembly when engaged bysaid grommet upon depression of said key with sufficient force toovercome the magnetic force holding said key in said non-actuatableposition, said grommet having a first ring means for first contactingsaid spaced-apart contacts upon initial engagement therewith and acenter portion for further engaging said contact pad upon furtherdepression of said key, said ring and said center portion beingseparated by a resilient web.
 7. The grommet as claimed in claim 6wherein said outer ring slidably engages said spaced-apart contacts assaid center portion moves toward engagement with said contact pad.
 8. Amagnetic keyboard comprising: mounting means of magnetic Material havingan opening therein; a key assembly including a key stem reciprocablymounted in said opening and a key top mounted at one end of said stem,said key assembly adapted to be reciprocated between a non-actuatedposition and an actuated position; magnetic means on said key stem andlocated on the opposite side of said mounting means from said key top;spacer means positioned between said mounting means and said magneticmeans for providing a predetermined maximum holding force therebetweenwhen said key is in said non-actuated position; a base member spacedfrom said mounting member and having an opening adapted to slidablyreceive one end of said key stem; a contact pad with spaced-apartcontact means located on the side of said base member facing said spacermeans; resilient electrically conductive means mounted on said key stembetween said magnetic means and said base member and engageable withsaid spaced-apart contact means when said key is in its actuatedposition to electrically connect said spaced-apart contact means; saidresilient electrically conductive means comprising; a grommet having anouter ring and a center portion separated by a resilient web, thesurface of said ring facing said contact pad being closer to saidcontact pad than the surface of said center portion facing said contactpad so that said outer ring first slidably engages said spaced apartcontact means as said center portion moves toward engagement with saidcontact pad, the reaction force of said ring initially engaging saidcontact means being transmitted through said resilient web to said keystem and key top to provide the first step of a two-step touch to anoperator, and engagement of said center portion with said contact pad,and to provide the second step and stop touch to the operator, saidengagement of said center portion being directed to said key topindependently of said resilient web whereby continued pressure by theoperator on said key top is not transmitted to said ring, therebyeliminating possible damage to said spaced apart contact means by suchcontinued pressure of the operator.